1. Field of the Invention
This invention relates to polymeric modifying agents having temperature-dependent properties.
2. Introduction to the Invention
It is known to control the rate of a chemical reaction by providing a reactant, a catalyst or other active agent in a modified form such that the availability of the active agent depends upon some external factor. For example, the active agent can be encapsulated by a protective shell which at least partly prevents access to the active agent. When release of the active agent or an increase in its concentration is desired, the shell is removed, or the shell is subjected to a treatment which does not destroy its physical integrity (i.e. the shell resins its shape and is not free to flow during the treatment), but which increases the rate at which the active agent can permeate through the shell. Removal of the shell can be effected, for example, by means of heat, solvent, or ultrasonic waves. A change in the permeation rate can, for example, be effected by using a shell having temperature-dependent permeability and by changing the ambient temperature; for further details of particularly useful temperature-dependent systems of this kind, reference may be made, for example, to commonly assigned U.S. Pat. Nos. 4,830,855 (Stewart), 5,129,180 (Stewart) and 5,254,354 (Stewart), the disclosures of which are incorporated herein by reference for all purposes.
It is also known to use so-called "latent hardeners" or "latent curing agents", optionally in conjunction with "latent accelerators". These "latent" compounds can be mixed with the other ingredients for a crosslinked resin, e.g. an epoxy resin or a polyurethane, to give compositions which are relatively stable at room temperature but which cure rapidly when heated to an elevated temperature, e.g. 160.degree. C. or more. Systems of this kind are disclosed for example in U.S. Pat. Nos. 4,349,651 (Smith), 4,358,571 (Kaufman et al), 4,420,605 (Kaufman), 4,430,445 (Miyake), 4,659,779 (Bagga et al), 4,689,388 (Hirai et al), 4,701,378 (Bagga et al), 4,742,148 (Lee et al) and 4,933,392 (Andrews et al), and European Patent Publication No. 362787 A2 (Henkel), the disclosures of which are incorporated herein for all purposes.
Many attempts have been made to develop systems which are stable for extended periods at storage temperatures, but which will cure rapidly when heated to give crosslinked polymers having desired properties. However, only limited success has been achieved.
It is also known to prepare polymers containing reactive moieties which will react with other materials under appropriate conditions. For example, in the materials often referred to as "polymer-supported catalysts", the reactive moiety is one which provides a catalytic function. Reference may be made, for example, to Encyclopedia of Polymer Science and Engineering, Vol 2, pages 702-729, the disclosure of which is incorporated herein by reference for all purposes.